1. Field of the Invention
This invention relates to a resin bonded abrasive tool particularly useful, for example, for mill grinding of hard and brittle.
The disclosure of Japanese Application No. H11-230909, H11-246748, and 2000-038653 is hereby incorporated by reference into the present application.
2. Description of the Background
Generally, resin bonded abrasive tools are produced by the following method. The raw powders of thermosetting resin, such as, for example, an epoxy resin and phenol resin, are mixed with the super abrasive grains of a diamond and CBN, etc. This mixture is molded independently, or with a base metal if needed. Then, it is pressed and sintered. The result is a resin bonded abrasive tool having a super abrasive grains layer.
When the grinding is performed to comparatively hard work materials, the resin bonded phase holding super abrasive grains is crushed or worn out. Super abrasive grains drop out rather than decrease in sharpness by the wear in a tip of the super abrasive grain, because, in resin bonded tool, the resin bonded phase holding the super abrasive grains is comparatively elastic and brittle. Therefore, although resin bonded tools are susceptible to intense wear, clogging on a surface of grinding and a decrease in sharpness of a super abrasive grain due to wear are not common. Thus, resin bonded tools are able to perform grinding efficiently as compared with metal bonded tool, etc. Moreover, the damage to work materials is small and the finished surface is good, due to the elastic effect of the super abrasive grains held by resin bonded phase. Therefore, it has the advantage of being used for the grinding where small surface roughness such as mill grinding of work materials of semi conductor wafer for example is required. By the way, in the conventional resin bonded tool, solid lubricant, such as hBN and graphite for example, is dispersed inside of the resin bonded phase as filler in order to control the frictional heat generated by grinding resistance.
For example, in resin bonded tool 1 shown in FIG. 9, diamond abrasive grain 4 dispersed inside of resin bonded phase 3 consisted of phenol resin as grain layer 2. Solid lubricant 5 such as CaF2 (calcium fluoride), etc. is added and further distributed. In case of the grinding by using these resin bonded abrasive tool, the solid lubricant 5 inside of resin bonded phase 3 has a function as lubricant in omitting one by one with resin bonded phase 3 and abrasive grain 4 and aids smoothly performed grinding by a super abrasive grain 4. The solid lubricant 5 may also aid in controlling the friction heat of grain layer 2 and work material.
However, although cutting resistance can be reduced by the addition of solid lubricant which is distributed as filler in resin bonded abrasive tool of above mentioned composition, the problem remains that the life of abrasive tool is short by the reason that the binder phase of resin is brittle. Also, increasing the wear resistance of abrasive particle layer is difficult to achieve. This invention aims at offering resin bonded abrasive tool which can raise wear resistance and reduce the grinding resistance.
In order to attain the purpose which solves the above mentioned subject, the resin bonded abrasive tool of this invention is characterized by distributing amorphous carbon in the above mentioned resin binder phase in resin bonded abrasive tool which comes to distribute super abrasive particle in resin binder phase. The amorphous carbon (also referred to as xe2x80x9cglassy carbonxe2x80x9d) has the characteristics that the bending strength is at about 16 kg/mm2, a value about 5 times to graphite (xe2x80x9calso referred to as xe2x80x9ccrystal carbonxe2x80x9d). Also, the compressive strength is at about 120 kg/mm2, a value about 20 times greater than for graphite. The modulus of elasticity is about 3 times greater than for graphite, and the shore hardness Hs is at about 110, a value about 3 times greater than for graphite. Here, the binder phase of resin bonded abrasive tool is made, for example, from phenol resin, the modulus of elasticity of the phenol resin is at about 7xc3x97102 kg/mm2, The rate of modulus of elasticity of abrasive particle layer of resin bonded abrasive tool can be raised by adding and distributing amorphous carbon in resin binder phase of resin bonded abrasive tool. This can raise the compressive rigidity of abrasive particle layer. Also, the abrasive particle layer can carry out compressive deformation by grinding resistance at the time of grinding, or it can prevent super abrasive particle from being buried into resin binder phase even where the super abrasive particle projects from the surface of abrasive particle layer and forms the cutting tooth of resin bonded abrasive tool which receives the grinding resistance. Further, the mechanical strength of abrasive particle layer holding super abrasive particle can be raised. Furthermore, the amorphous carbon distributed in resin binder phase acts as lubricant, can reduce the grinding resistance between work materials, and can control the generation of grinding heat. In addition, for example, it can control more effectively the deformation of resin bonded abrasive tool, or the wear of the tool because the hardness, compressive strength and bending strength of amorphous carbon is large compared with solid lubricant such as graphite. Furthermore, the resin bonded abrasive tool in this invention has the characteristics that the above mentioned amorphous carbon is the shape of spherical type. In above mentioned resin bonded abrasive tool, spherical amorphous carbon can raise the compressive strength of resin binder phase, and it also relieves the stress which acts to the abrasive particle layer at the time of grinding machining.
Moreover, as the spherical amorphous carbon exposed from the surface of abrasive particle layer contacts the grinding surface of work materials, the frictional resistance is small and the generation of frictional heat is suppressed small even if the friction with the work materials arises. Moreover, if the resin binder phase which holds spherical amorphous carbon on the surface of abrasive particle layer is worn out and approximately half grade of the whole volume of the spherical amorphous carbon comes to project from the surface of abrasive particle layer, this amorphous carbon will be omitted from the surface of abrasive particle layer, and a tip pocket will be formed in the position where the amorphous carbon was held. That is, compared with non uniform shape particles by which unevenness was formed, for example, on the outside surface, amorphous spherical carbon promotes a decrease in the holding force by resin binder phase and omission from resin binder phase. The discharge ability of scraps improves in that the grinding liquid is introduced at the time of grinding machining or grinding waste etc. enters into the formed tip pockets.
On the other hand, as the amorphous carbon is spherical, the compressive strength is high compared with non uniform type, the grinding load and the deformation by grinding can be controlled, and it can prevent effectively burying into the resin binder phase of super abrasive particle which exists in the outside surface. Furthermore, the mobility and formability of raw materials can be raised in case that the abrasive particle layer is formed. Furthermore, the resin bonded abrasive tool has the characteristics that the above mentioned amorphous carbon is non uniform shape.
In resin bonded abrasive tool mentioned above, particularly, in case that the minute amorphous carbon is dispersed in resin binder phase, the spherical amorphous carbon is in the tendency of dropping out from resin binder phase. The holding force can be raised by using the amorphous carbon of non uniform shape. Furthermore, the resin bonded abrasive tool in this invention has the characteristics that the amorphous carbon of the above mentioned non uniform shape results from grinding spherical amorphous carbon. Although the minute and spherical amorphous carbon has the problem that the manufacture is difficult and moreover tends to drop out from resin binder phase, for example, the non uniform shape amorphous carbon which has a particle size distribution which is shown in FIG. 7 can be obtained easily by crushing the spherical amorphous carbon against that the mean particle diameter about 20xcx9c30 xcexcm shown in Table 1 and FIG. 10. The holding force by resin binder phase can be raised and the wear resistance of resin bonded abrasive tool can be raised.
And the spherical amorphous carbon is the most precise and the precise and minute shape amorphous carbon can be obtained by crushing the spherical amorphous carbon. Furthermore, the resin bonded abrasive tool in this invention has the characteristics that the particle diameter of above mentioned non uniform shape amorphous carbon is 20 xcexcm or less. If the particle diameter of the amorphous carbon of non uniform shape distributed in resin binder phase exceeds 20 xcexcm in above mentioned resin bonded abrasive tool, the contact length of work material and resin may increase and the grinding resistance may increase. However, by setting particle diameter to 20 xcexcm or less, the amorphous carbon is arranged in a narrow pitch and the contact of the work material and resin is controlled. As a result, the grinding resistance is reduced and the generation of grinding heat is controlled. Also the wear resistance of resin bonded abrasive tool can be raised. Furthermore, the resin bonded abrasive tool of this invention has a characteristic that the metal of Cu or Ag or Ni or Co or alloy including these metals is coated on a surface of above mentioned amorphous carbon. In above mentioned resin bonded abrasive tool, the amorphous carbon coated by metal which is a high thermal conductivity is distributed in abrasive particle layer. As a result, the thermal conductivity of abrasive particle layer can be raised, the heat which occurs at the time of grinding machining can be made to be able to emit quickly from abrasive particle layer, and the deterioration of resin binder phase can be prevented. Furthermore, the resin bonded abrasive tool in this invention has a characteristic that the volume ratio of above mentioned amorphous carbon to the above mentioned resin binder phase except super abrasive particle is 5xcx9c60 vol %. In above mentioned resin bonded abrasive tool, if the amorphous carbon becomes less than 5 vol %, the effect which controls the generation of the wear heat based on the decreasing of grinding resistance and improve the wear resistance of abrasive particle layer is weak where the volume exceeds 60% conversely, since the the ratio of resin binder phase which occupies in abrasive particle layer will decrease, the strength of the abrasive particle layer decreases. The wear resistance of abrasive particle layer also decreases, and economical efficiency falls. Furthermore, the resin bonded abrasive tool in this invention has a characteristic that the hardness of amorphous carbon is Hs=100xcx9c120 inshore hardness scale. In above mentioned resin bonded abrasive tool, the amorphous carbon is produced by baking phenol formaldehyde resin at 500xc2x0 C.xcx9c3000xc2x0 C. If it is baked below 600xc2x0 C., the shore hardness becomes less than 100, and since the hardness of amorphous carbon is small, the deformation of the resin bonded abrasive tool and inclination wear can not be controlled. Also, since the lubricity is low, the generation of grinding heat by the decreasing grinding resistance between work materials cannot be controlled. On the other hand, hardness is as high as which was baked at high temperature, and it serves as amorphous carbon excellent in lubricity. Furthermore, the resin bonded abrasive tool in this invention has a characteristic that at least one wear resistant filler can be present in the above mentioned resin binder phase. In this resin bonded abrasive tool, hard wear resistant filler is also distributed. As a result, the strength of the abrasive particle layer is raised, wear can be reduced and amorphous carbon is distributed. As a result, the decreasing of grinding resistance is decreased without decreasing the grinding ratio. Furthermore, the resin bonded abrasive tool in this invention has a characteristic that the above mentioned wear resistant filler includes at least one of SiC, SiO2, Ag, Cu, Ni. In above mentioned resin bonded abrasive tool, since at least one of SiC, SiO2, Ag, Cu, Ni as the filler is included, the wear of abrasive particle layer is controlled much more, and prolongation of abrasive tool life can be controlled. Furthermore, the resin bonded abrasive tool in this invention has a characteristic that at least one lubricative filler is distributed in resin binder phase. In above mentioned resin bonded abrasive tool, since the lubricative filler is distributed, the grinding resistance is reduced. The grinding ratio can be raised without increasing grinding resistance by distributing amorphous carbon to resin bonded abrasive tool with the sufficient sharpness planned so that the grinding of the work material by super abrasive particle could be smoothly performed at the time of grinding. Furthermore, the resin bonded abrasive tool in this invention has a characteristics that the above mentioned lubricative filler includes at least one of graphite, hBN, or fluoro-resin. In above mentioned resin bonded abrasive tool, since at least one of graphite, andd hBN, fluoro-resin can be lubricative filler, the grinding resistance is reduced much more. Thus, the resin bonded abrasive tool which is excellent in sharpness and, which can perform the grinding of work material smoothly can be obtained. Furthermore, the resin bonded abrasive tool in this invention has a characteristic that the pores are included 5xcx9c40 vol % in resin binder phase. In this resin bonded abrasive tool, the pores have effects such as inducing the grinding liquid on a surface of abrasive particle layer, improving the discharge ability of tip, and preventing condensation with work material. As a result, by the synergistic effect with the amorphous carbon, grinding resistance is reduced much more and there is a remarkable effect in an improvement of the grounded surface roughness of work material. Here, if the pore volume is less than 5 vol %, the effect mentioned above is weak. In case that the pore volume exceeds 40 vol %, the strength of the abrasive particle layer will decrease. Furthermore, the resin bonded abrasive tool in this invention has a characteristic that the hollow glass is distributed in resin binder phase. In this composition, the part of the hollow glass exposed from the surface of the abrasive particle layer is destroyed by the contact with work material at a time of grinding. As a result, the tip pocket is formed and the discharge ability of the tip can be improved, and in addition, the strength of the abrasive layer that was decreased by the addition of hollow glass can be raised by the addition of amorphous carbon simultaneously. It can be possible to obtain the resin bonded abrasive tool excellent to the sharpness. In addition, where the lubricative filler is distributed in resin binder phase adding to hollow glass, (although there are the case where the strength decreases even to the state where the strength of abrasive particle layer becomes weak much more and practical use is not possible, for example, by exchanging a part of lubricative filler such as graphite to amorphous carbon), the strength of abrasive particle layer, in particular, the compressive strength can be raised, and the resin bonded abrasive tool excellent to the sharpness can be obtained.